As far as I can tell, band names are typically treated as a plural if the name of the band starts with "the" and is a plural noun or based around a plural noun -- or more generally, if it seems to be referring to its members as a collection of entities -- and a singular otherwise. So we would have:

The Beatles are a great band.

Korn is a great band.

The Rolling Stones are a great band.

Metallica is a great band.

Led Zeppelin is a great band.

Nine Inch Nails is a great band. (note that the plural noun does not control here)